TUN-1615: revert miekg/dns to last known working revision

The last known good commit is 6da3249dfb57fbaa16efafcd8744cee8809d80cd before the first release tag.

vendor/golang.org/x/net/ipv4/helper.go

@@ -1,64 +0,0 @@
-// Copyright 2012 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package ipv4
-
-import (
-	"errors"
-	"net"
-)
-
-var (
-	errInvalidConn              = errors.New("invalid connection")
-	errMissingAddress           = errors.New("missing address")
-	errMissingHeader            = errors.New("missing header")
-	errHeaderTooShort           = errors.New("header too short")
-	errBufferTooShort           = errors.New("buffer too short")
-	errInvalidConnType          = errors.New("invalid conn type")
-	errOpNoSupport              = errors.New("operation not supported")
-	errNoSuchInterface          = errors.New("no such interface")
-	errNoSuchMulticastInterface = errors.New("no such multicast interface")
-
-	// See http://www.freebsd.org/doc/en/books/porters-handbook/freebsd-versions.html.
-	freebsdVersion uint32
-)
-
-func boolint(b bool) int {
-	if b {
-		return 1
-	}
-	return 0
-}
-
-func netAddrToIP4(a net.Addr) net.IP {
-	switch v := a.(type) {
-	case *net.UDPAddr:
-		if ip := v.IP.To4(); ip != nil {
-			return ip
-		}
-	case *net.IPAddr:
-		if ip := v.IP.To4(); ip != nil {
-			return ip
-		}
-	}
-	return nil
-}
-
-func opAddr(a net.Addr) net.Addr {
-	switch a.(type) {
-	case *net.TCPAddr:
-		if a == nil {
-			return nil
-		}
-	case *net.UDPAddr:
-		if a == nil {
-			return nil
-		}
-	case *net.IPAddr:
-		if a == nil {
-			return nil
-		}
-	}
-	return a
-}